1. Field of the Invention
The present invention relates to a semiconductor photoelectric transducer.
2. Description of the Prior Art
Semiconductor photoelectric transducers are known diodes, such as a p-i-n photo proposed by one of the inventors of the present invention, and an avalanche photo diode and so on. Further, a bipolar phototransistor and the like are also known. The inventors of the present invention have proposed, as high-sensitivity, high-speed and low-noise phototransistors, a field effect transistor and a static induction transistor (hereafter referred to as an SIT) which are provided with a channel having a low impurity density or formed of an intrinsic semiconductor in Japanese Patent Application Nos. 86572/78 (U.S. Ser. No. 39,445), 87988/78 (Laid-Open Publication No. 19229/80) and now U.S. Pat. No. 4,427,990, 192417/81 (U.S. Ser. No. 522,307 and European Patent Application No. 829034768), 194286/81 (U.S. Ser. No. 522,153 and European Patent Application No. 82-903,477.6) for infrared light detection and 153429/81 (PCT/JP83/00295) for improved structure. These photoelectric transducers are very high-sensitivity and high-speed, and hence are very excellent in characteristic as compared with the conventional bipolar phototransistors.
FIGS. 1A to 1D illustrate prior semiconductor photoelectric transducers proposed by the inventors of the present invention, which are provided with at least one or more gates. Reference numeral 1 indicates an n.sup.+ substrate of silicon; 2 designates a low-resistivity n-layer or an i layer of an intrinsic semiconductor which will ultimately serve as a channel; 3 identifies a first gate region of high impurity density and reverse in conductivity type from the channel; 4 denotes a second gate region of high impurity density and reverse in conductivity type from the channel as is the case with the first gate region 3; 5 represents a high impurity density region of the same conductivity type as the substrate 1; 7 and 10 respectively show electrodes of the substrate 1 and the region 5 which form a main current path of the channel; 8 refers to a gate electrode of the first gate region 3; 9 signifies a gate electrode of the second gate region 4; and 6 indicates a multilayer film as of SiO.sub.2, Si.sub.3 N.sub.4 or the like which forms an insulating film layer or insulating layer which performs known functions of insulation for isolating the electrodes 7, 8 and 9 and provides surface protection.
With the prior semiconductor photoelectric transducer shown in FIG. 1A, since the first and second gate regions 3 and 4 are provided symmetrically with respect to the main electrode region 5, diffusion potentials between both gate regions 3 and 4 and the main electrode region 5 are equal to each other, making it difficult to separate the functions of the two gates. The prior semiconductor photoelectric transducers shown in FIGS. 1B and 1C have the structure that the distance W.sub.1 between the first gate region 3 and the main electrode region 5 is larger than the distance W.sub.2 between the second gate region 4 and the main electrode region 5, thereby facilitating the storage of optically excited carriers in the first gate region 3 alone. These semiconductor photoelectric transducers are excellent in optical characteristics as compared with the semiconductor photoelectric transducer depicted in FIG. 1A.
FIG. 1D schematically shows the outline of the surface of such a prior semiconductor photoelectric transducer. Reference numeral 8 indicates the electrode region of the first gate region 3, 9 the electrode region of the second gate region 4 and 7 the electrode region of the main diffused electrode region 5. With such a electrode pattern, it has been clarified that since the distances between the gate regions 8 (3) and 9 (4) and the main electrode region 7 (5) differ from each other, the parts 30 surrounded by the broken lines and the non-surrounded parts differ in channel width to cause variations in the characteristic of the SIT, making it impossible for the SIT to direct the current uniformly in the channel.